Arc Lamps comprise electrodes which are separated by a distance in a sealed volume in which is contained a gas which, when energized, emits electromagnetic radiation typically comprising a spectrum of wavelengths. The effective origin point of the beam is, of course, located between said electrodes, and said effective origin point can vary over time. Where such an Arc Lamp is utilized to direct a beam of electromagnetic radiation at a sample surface at an oblique angle, the precise measure of said oblique angle can vary with the origin point of the beam, and, as the Arc Lamp ages, the origin point of the beam can vary in position between the electrodes.
With the present invention in mind, a Search of Patents was conducted. As the present invention is a system which comprises a plurality of reflecting means which rotate a “vertically” oriented beam into a “horizontally” oriented beam in ellipsometer and the like systems, the Search was focused on ellipsometer and the like systems which comprise a plurality of reflective means.
The following Patents all describe ellipsometer or the like systems which comprise a plurality of reflective means:
                U.S. Pat. No. RE38,253 to Finarov;        U.S. Pat. No. 6,714,301 to otsuki et al.;        U.S. Pat. No. 6,753,962 to Opsal et al.;        U.S. Pat. No. 5,229,833 to Stewart;        U.S. Pat. No. 4,790,659 to Erman et al.;        U.S. Pat. No. 4,210,401 to Batten;        U.S. Pat. No. 5,963,327 to He et al.;        U.S. Pat. No. 6,795,184 to Herzinger et al.        U.S. Pat. No. 4,681,450 to Azzam;        U.S. Pat. No. 4,332,476 to Stenberg et al.        Published Application No. US 2004/0085538 A1 by Hovinen et al.;        Published Application No. US 2002/0159063 A1 by Kanzaki.        
While many references describe causing a beam of electromagnetic radiation to undergo a plurality of reflections in ellipsometer or the like systems, none suggest utilizing a plurality of reflecting means to rotate the locus of an Arc lamp arc from substantially vertical to substantially horizontal, in order to prevent lamp aging from changing the effective angle-of-incidence of a beam of electromagentic radiation produced by said Arc lamp, with respect to a sample surface.